Some internal combustion engines (ICEs) are designed to operate on natural gas fuel. Such natural gas fueled ICEs may be dedicated natural gas engines, or multi-fuel engines. A dedicated natural gas engine operates only on natural gas. A multi-fuel engine is capable of operating on multiple fuel types. For example, bi-fuel engines are capable of operating on two different fuel types. One fuel type may be a liquid phase fuel including gasoline, ethanol, bio-diesel, diesel fuel or combinations thereof that are delivered to the bi-fuel engine substantially in a liquid state. The other fuel type may include an alternative fuel, e.g., Compressed Natural Gas (CNG), Adsorbed Natural Gas (ANG), Liquefied Petroleum Gas (LPG), hydrogen, etc. The two different fuels are stored in separate tanks, and the bi-fuel engine may run on one fuel at a time, or may alternatively run on a combination of the two different fuel types.
Natural gas may be stored on a vehicle in several ways. Some vehicles store the natural gas in pressurizable tanks. Some vehicles have a natural gas adsorbent in the natural gas tanks to increase the mass of natural gas that may be stored in the tank at a lower pressure. ANG is distinguished from CNG which is stored in pressurized vessels without adsorbent.